IDMR Working Group                                   Tissa Senevirathne
Internet Draft                                        Sridhar Vallepali
Document: draft-tsenevir-pim-sm-snoop-00.txt
Category: Informational                                Force10 Networks
                                                            April, 2002

      Protocol Independent Multicast-Sparse Mode (PIM-SM) Snooping

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
      all provisions of Section 10 of RFC2026 [1].

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   For potential updates to the above required-text see:


   This document provides PIM-SM snooping solution. In the document we
   present the framework and reference model and required PIM-SM
   messages for PIM-SM snooping solutions. Also we attempt to discuss
   related issues to PIM-SM snooping.

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Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC-2119 [2].

1. Introduction

   IGMP snooping is popularly used to limit the scope of IP multicast
   traffic in enterprise Local Area Networks (LAN). With the recent
   popularity of Layer 2 Networks in core of the networks, PIM-SM
   snooping is gaining popularity as a way of constraining IP multicast
   traffic to the section of network that is interested in receiving
   such traffic.

       |                                     |
       |                                     |
     ------                               --------
    |       |                            |        |
    | PIM-R |                            | PIM-R  |
     ------- \                         /  --------
              \    Multicast Routed   /
      ---------\-------------------- / -----------
                -----         ------/
               |  S  |       |  S   |  Layer 2 Switched/Bridged
               |     |-------|      |
              /  -----        ------ \
    -------- / ---------------------  \---------------
    ------- /   Multicast Routed       \ --------
   |       |                            |        |
   | PIM-R |                            | PIM-R  |
    -------                              --------
       |                                     |
       |                                     |

   PIM-R  - PIM-SM Routers

   S      - PIM-SM Snooping Device

   Fig: Reference Model of PIM-SM snooping

2. PIM-SM Snooping Framework

   Devices that implement PIM-SM snooping are required have ability to

   1. Intercept Join/Prune messages [3]
   2. Ability to create IP Multicast scope per VLAN (Virtual LAN)
   3. MUST not have impact on other Multicast traffic
   4. MUST not modify packet content (such as TTL..) or in other words
   MUST be forwarded using Layer 2 forwarding rules.

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3. Theory of Operation

   Let assume that

   VLAN V has interfaces I == {i1, i2,}

   Let assume we identified, by snooping PIM-SM join messages, that
   interface set G need to join (*,G) or (S,G). These interfaces Let
   call outgoing interfaces.

   G == {o1, o2,}; G subset of I.

   Now create a sub-scope S within the VLAN such that

   input interfaces == I and
   out put interfaces == G

3.1 Maintaining outgoing interfaces

   outgoing interface (o) is added to the list when a join message is
   received from that interface.

   When an interface is added to the G a Hold timer is created for each
   interface. Periodic Join messages update the life.

   When there are more than on Join is received from a given interface
   the largest hold time MUST be used.

   When hold time expires the interface SHOULD be removed from that
   group for that VLAN.

   When a Prune message is received the interface SHOULD be removed
   from that group for that VLAN.

   If more than one Join message was received from an interface and a
   Prune message is received the Hold timer MUST be update according to
   the other active Joins.

3.2 (*,G) vs (S,G)

   Devices that perform PIM-SM snooping is practically operating as a
   Layer 2 device. When PIM-SM is not implemented entire VLAN is the IP
   Multicast scope. The scope of PIM-SM snooping is to constrain the IP
   Multicast data flooding. As such, PIM-SM snooping does not attempt
   to disnguish between (*,G) and (S,G). In effect PIM-SM snooping
   implement (V,G). Where V is all interface of the VLAN V. Such
   generalization, simplify the implementation; servers the purpose and
   avoid blackholes when IP routing changes the RPF inetrfaces.

4. Security Considerations

   PIM-SM snooping does not affect the security aspects of PIM-SM.

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5. References

   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

   2  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

   3 Estrin, D.,, Protocol Independent Multicast-Sparse Mode
      (PIM-SM): Protocol Specification, RFC 2362, June 1998.

10.  Acknowledgments

11. Author's Addresses

   Tissa Senevirathne
   1440 McCarthy Blvd
   Milpitas, CA
   Phone: 408-965-5103

   Sridhar Vallepali
   1440 McCarthy Blvd
   Milpitas, CA
   Phone: 408-571-3500

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Full Copyright Statement

   "Copyright (C) The Internet Society (2002). All Rights Reserved.
   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implmentation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into

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